Lighting devices based on light-emitting diodes are currently contemplated for indoor illumination, such as for example in offices, homes, stores, automobiles and airplanes, etc.
Conventionally, fluorescent tubes and incandescent lamps have been used as light sources for such lighting devices.
Lately, light-emitting diodes (LEDs) have been proposed as light sources for this type of lighting devices. Light-emitting diode based lighting devices are attractive since the life time of a light-emitting diode typically is much longer than the lifetime of fluorescent tubes and incandescent bulbs. Furthermore, light-emitting diodes are less power consuming than incandescent bulbs, and are expected to become more efficient than fluorescent tubes in the future.
The development of high-power LEDs, providing light-emitting diodes emitting very high intensity light, intensifies this progress.
One example of a LED-based overhead lighting system is described in U.S. Pat. No. 6,764,196 to Bailey, which features a ceiling panel with a plurality of embedded ultra bright LEDs to illuminate a room. However, the lighting system described in U.S. Pat. No. 6,764,196 is not suited for displaying visually distinct information on the illuminated surface.
For projecting visually distinct, user interactive information, such as alphanumerical signs, images, patterns and video sequences, conventional data projectors are suitable.
However, conventional data projectors are typically based on a constantly operating high intensity discharge bulb and a programmable filter for switching individual pixels on or off. Thus, conventional data projectors would be very power consuming devices for indoor illumination.
Thus, there is a need for a lighting device that has low power consumption and which may be used both for ambient illumination and information projection.